Such weighing sensors are advantageously arranged in a circle, wherein it is attempted to accommodate a maximum of weighing cells in as small a circular arc as possible in order to save overall space.
Rotary filling heads, as in DE 20304296 U1, for example, in which numerous filling stations are arranged in a circle, are known in the beverage industry; since they can be continuously filled, such heads make high product throughput possible. These filling machines have a filling head with a flow controller that portions out the respective desired amount of the material to be filled.
Volumetric rotary filling heads are known for pourable bulk material. The filling head is adjusted corresponding to the density of the material to be filled, and a constant volume is directed into the corresponding container to be filled. The disadvantage of these filling systems lies in the density variation of the supplied products. For example, detergents can be conducted from the silo or directly from the flocculating system to the filling system, and thus have a differing density due to the different pile heights. Moreover, the volume ranges, and thus the weight ranges of the material to be filled, are limited, i.e., such systems can be operated only with a limited measurement range. Volumetrically operating rotary filling heads usually have a downstream monitoring scale, which checks the filling weight of the packages and readjusts the filling head amount accordingly. The disadvantage of these filling systems lies in the control weighing process that takes place relatively far away from the actual filling process, which entails a higher defect rate for products with incorrect weights due to the time delay of the downstream monitoring scale.
According to prior art, rotary filling heads are known that are based on weighing technology by means of DMS. The disadvantage appearing here is the long settling time of the DMS weighing cell upon load input. This property is further intensified by the rotation of the complete filling head. Furthermore, DMS weighing cells exhibit bending with an increasing load, which must be alleviated in prior art (DE 372 78 66 C2) by an additional correction cell, for example.
During the installation of weighing equipment in the head of a rotationally operating filling machine, problems arise with the installation conditions of a measuring cell. Weighing cells typical in prior art have a cuboid housing; when they are being inserted into a divided circle, one recognizes that the smallest possible divided circle diameter is severely limited by the geometric shape of the measuring cell.
The weighing cells disclosed in prior art in EP 1 409 971 B1 with a wide threaded connection to the stationary base and a trapezoidal parallelogram guidance are not suitable for inclusion in a divided circle.
EP 518202 B1 discloses a weighing sensor in which the individual functional units of the block system are implemented by means of thin sections. The illustrations show a narrowly constructed weighing sensor; there is again the problem that the force-compensating magnet system represents the largest width of the system and, as is known from prior art, lies opposite the load receiving side. Here as well, the divided circle diameter is decisively determined by the magnet arrangement.
The length dimensions of the weighing cells entail another disadvantage. Prior art demonstrates weighing cells that comprise a parallelogram load sensor, wherein the elastic transmission that reduces the magnitude of an applied force is constructed between the upper and lower arms of the parallelogram. Prior art demonstrates various weighing sensors with up to 4 transmission ratio stages, with very high-ratio systems of up to 1500:1 being primarily found in static applications.
The weighing sensors known from prior art are designed with a compensation lever that is extended up to the compensation system. In the case of electromagnetic force compensation, this is a system consisting of a coil and a permanent magnet system. The magnet is arranged downstream of the step-down transmission, as described, e.g., in DE 19923207 C1. The upper and lower parallelogram arms, among other things, are constructed on the fixed part.
For monolithic weighing systems produced by machining, prior art therefore presents a spatially successive arrangement of load receiver, transmission lever, stationary base element and magnet system. Prior art further displays a magnet surrounded by block material in order to achieve a very high measuring precision for the system. It is evident here to a person skilled in the art that such a system is not suitable for a circular arrangement with the objective of the smallest possible divided circle diameter
A design with a magnet arranged between the two parallelogram beams (e.g., in DE 3243350 C2) can indeed be arranged in a space-saving manner, but the lever principle and the limited transmission ratio of the system in this arrangement limits the use to a very limited weight range.
The essential factor for the suitability of a weighing sensor based on the principle of electromagnetic compensation is the construction of as narrow an overall shape of the weighing cell as possible. The disadvantage of such a design lies in the weakening of the Roberval transmission with respect to torsion perpendicular to the force induction in the transverse direction passing through the block system. It is known from prior art that monolithically constructed weighing sensors are advantageously constructed with a coupling element, consisting of an intermediate web and two thin sections, between the load receiver and the first lever (and the additional transmission levers). Another advantageous design in prior art has been to construct a thin section in the first coupling rod in the longitudinal direction of the load receiver in order to avoid torsional torques on the transmission levers. As an example, one can refer in this regard to the publication EP 291 258 A2, especially FIG. 2.
The combination of a narrow Roberval transmission (for forced parallel guidance of the load receiver) and the thin section formed as mentioned above leads to a weighing sensor with low torsional rigidity in case of eccentric force introduction transverse to the block. It was therefore mentioned in EP 1550849 A2 that the parallelogram arm be constructed correspondingly wider than the block system, which represents a considerable extra expense compared to the weighing sensor originally constructed primarily in two dimensions.